1. Field of the Invention
The present invention relates to a Wireless Tag that can cope with the situation where the communication electric waves differ in frequency from place to place, and a method of reading data from the Wireless Tag.
2. Description of the Related Art
In recent years, Wireless Tags, each storing an ID, have come into use. The Wireless Tag has a memory area in and from which the ID and any desired data can be written and read by wireless, without setting the tag into contact with a data write/read device. For example, Wireless Tags using the UHF-band electric waves have come into use in international physical distribution, such as international mail, international freight, and baggage inspection at international airports.
However, the frequency at which data is written into and read from Wireless Tags differs from area to area. For example, the frequency used in Europe ranges from 866 to 870 MHz, the frequency used in the United States ranges from 902 to 928 MHz, and the frequency used in Japan ranges from 950 to 956 MHz.
Consequently, the data written into a Wireless Tag in, for example, Europe cannot be read at all. If the data is read in Japan, it will be incorrect, due to the low data-reading accuracy. This raises a problem.
To solve the problem, the resonance frequency allocated to the antenna of the Wireless Tag may be adjusted. More precisely, a dielectric member may be attached to the antenna, or the dielectric seal already adhered to the antenna is peeled off (refer to Jpn. Pat. Appln. Laid-Open Publication No. 2005-101706).
In the method of attaching a dielectric member to the antenna, however, an error may be made in the position or size of the dielectric member attached. Inevitably, it is difficult to adjust the resonance frequency with high accuracy. The method of peeling off the dielectric seal cannot achieve good results if the frequency of the electric waves greatly differs from area to area, as in the inspection of international cargo. This is because this method is to adjust the resonance frequency minutely if the data cannot be correctly read from the Wireless Tag. The method peeling off the dielectric seal can indeed lower the resonance frequency, but it cannot cope with the case where the resonance frequency should be raised. Further, in this method it is necessary to determine an appropriate amount in which to peel off the dielectric seal from the antenna.